I have no solid info on the issue, but have recently read two articles giving me pause.

The first is says "With the introduction of chlorine dioxide droplets or tablets to the market, now just about every little organism that causes sickness can be killed. The drawback is that required treatment time for cryptosporidium is 4 hours!" ( http://www.backpacking-guide.com/water-filter-purifier-reviews.html )

Second I read up on cryptosporidium. "It affects the intestines of mammals and is typically an acute short-term infection. It is spread through the fecal-oral route, often through contaminated water;[1] the main symptom is self-limiting diarrhea in people with intact immune systems. In immunocompromised individuals, such as AIDS patients, the symptoms are particularly severe and often fatal. Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea. Treatment is symptomatic, with fluid rehydration, electrolyte correction and management of any pain. Despite not being identified until 1976, it is one of the most common waterborne diseases and is found worldwide." (http://en.wikipedia.org/wiki/Cryptosporidiosis )

The same backpacking-guide article cites some filters which catch cryptosporidium.

1. ONLY the solid tablets contain sufficient concentration of chlorine dioxide to treat protozoa cysts (crypto, giardia, etc.) -- and yes, it can take between 30 minutes to a full 4 hours of treatment time -- the colder the water, the longer the time needed.

2. AquaMira liquids have just 1/3 the concentration of chlorine dioxide (feel free to read the labels on both). Read the AM liquids instructions and they mention ONLY treatment against bacteria -- NOT protozoa cysts. EPA regulations.

In talking to an AM customer rep, she said that folks can use the liquids to achieve the same effect as the solid tablets -- by quadrupling dosage. Don't know why tripling isn't good enough, but y'all can do the math.

Finally, I know numerous have reported they didn't get sick at all using AM liquids. But that's not following AM directions. Also, we all know of hikers who don't ever treat their water and didn't get sick. But neither is really a proof of anything...

If you're serious about killing the bugs, you'll zap them with this. Take backup tablets for incredibly murky water or battery failure, sure, but nothing beats drinking chlorine-free water in the wild, zapped to be perfectly sterile.

This is quite a simple theory and one that as an 3rd year environemental engineer I can explain however I dont have the formulas for chlorine dioxide solution however I have tried to explain for a typical chlorine solution as shown bellow. If you understand the theory, then the only difference would be number changes as the result of a differing chenmical reaction due to the addition to aqueous solution.

Typically the EPA removes Giardia to a 3-log and cryptosporidium to a 2-log, I have a table of figures for required CT of chlorine dioxide at varying water temperatures as outlined by the US EPA.

GIARDIATemp 0.5 5 10 15 20 25ClO2 CT 63 26 23 19 15 11

CRYPTOSPORIDIUMTemp 0.5 5 10 15 20 25ClO2 CT 1275 858 553 357 232 150

Using the above tables you should be able to determine a dose and time that suits your situation and removes these microorganisms, when using Clorine Dioxide. If you are interested in any other disinfectants CT's to relate ozone has the lowest acording to my material with CT's approximately 30 times lower.

@Nate: Nope. Remember, with UV you're not killing them; you're only mutating the organisms DNA to the point that it can't replicate, and then you're ingesting it live. Ingesting severely mutated bacteria, viruses, and protozoa FTW!!!

@Ben... you said you use bleach only and then use the fp filter... and you do this to save money...

i've read somewhere here that household bleach degrades and it's not as effective as it was when the container was first opened...

i still like the idea of the FP filter and from your posts and the post where shows the video of Jason showing the gravity setup... that's what i'll do...

Just to give my opinion on this matter... many people using drops, or tablets, just wait enough (15 to 30 mins) to get drinking water... i wonder if they would have gotten sick even if they did not treat their water...

I'll just be on the safe side and get the tables and then filter using the FP filter...

I don't worry about the freshness of my chlorine bleach supply because it gets used and replenished regularly in my household. Stored in a cool, dark place -- the chlorine efficacy should last 6 months (warmer temps can shorten this to just 3 months). Avoid buying in gargantuan gallon jugs to prevent the stuff from getting 'stale'.

If you rarely use bleach and you're worried that a bottle will just sit forever -- then consider buying chlorine in tablet form at any pool supply store. Click here to read more. Still cheap as heck and not too much of a hassle really -- and a lot better than getting fleeced $18 for a measly 20 chlorine dioxide tablets.

Aquatabs are not chemically the same thing. From their web site: "They are effervescent (self-dissolving) tablets, the US EPA approved active ingredient is NaDCC which is also known as Sodium Dichloroisocyanurate or Troclosene Sodium."

While Portable Aqua has Potable Aqua Chlorine Dioxide Water Purification Tablets and its active ingredients is clorine dioxide tablets.

See http://en.wikipedia.org/wiki/Chlorine_dioxide -- lots of references, etc. on this.

See http://en.wikipedia.org/wiki/Sodium_dichloroisocyanurate -- this is so new, hardly any information exists.

This newer product works in 30 minutes versus the worst case wait for the chlorine dioxide tablets of 4 hours (but only 20 minutes if you pre-filter with a 1 micron absolute filter for Giardia and Cypto. I like the .5 micron nominal filter for $4 that weighs 1 oz from DudaDiesel.com (use a wire clipper to remove the steel ring at top to get weight down to 1 oz).

http://www.dudadiesel.com/choose_item.php?id=PTFEP3S

I'd like to hear from more educated, chemically and biochemically, medically, about this newer chemical form.

I believe though this newer chemical is the cause for the one product no longer being distributed. REI has switched to this newer chemical:

The cootie-killing chemical created by Aquatabs is free chlorine, which isn't effective against cryptosporidium (nor is the iodine from the original Potable Aqua tablets). Chlorine dioxide is somewhat effective at neutralizing crypto, which makes it the best purification tablet available. Except that it doesn't seem to be currently available.

I know that Katadyne had production problems last spring for their Micropur tablets, due to moving their facilities to another location in Switzerland. They indicated that Micropur would be again be available in August, 2013. Hmmm...

Potable Aqua's chlorine dioxide tablets are claimed to be made in the U.S.A. and are distributed by Wisconsin Pharmacal Co. I found it interesting that the foil packaging of the Micropur and the Potable Aqua chlorine dioxide brands are nearly identical, with just 1-2 words on the directions being different. So this is likely an FDA wording requirement, or else both brands might possibly be made by the same manufacturer. Hmmm...

Last week I happened to drop into the store where I bought my Potable Aqua ClO2 tabs in June. They were also out of stock, and they had no clue as to when they would be receiving more. On the Potable Aqua site, they also indicated that it would be available sometime in August 2013. Another hmmm...

All I know is that I prefer chlorine dioxide to all other purification agents. And I'm glad that I stockpiled a bunch of it earlier this summer. With a stash of >100 tablets on a shelf in my basement, I should be good through next spring. But if nobody makes this available by then, I think one of you chemistry guys/gals should start your own company and produce it. For the common good of hikers planet-wide...